The use of ultrasonic sensors in an automobile, e.g., commonly known as reversing radars in an automobile, i.e., a front and rear parking assist system, is increasingly popular. The surrounding environments in front and back of the automobile are detected via ultrasonic sensors arranged in the front and the back of the automobile to judge objects and clear blind areas through the use of the ultrasonic detection technology and the ultrasonic sensors.
At present, the semi-automatic or automatic parking system (hereinafter collectively referred to as an automatic parking system) additionally applied to the automobile also detects the surrounding environments via ultrasonic sensors, and seeks and recognizes a parking plot via automatic parking sensors. The automobile blind spot monitoring system (or referred to as an automobile blind spot assist system) applied to some automobiles at present also adopts the ultrasonic detection technology, and it detects the blind areas that cannot be observed from the left and the right lane exterior mirrors of the automobile via blind spot sensors to assist the driver in changing lanes and driving.
As shown in FIG. 1, parking sensors 16 and 13 (also referred to reversing radar sensors) are provided and respectively arranged at different positions in the front and the back of an automobile, with four or two sensors in the front and four, three or two sensors in the back. Generally, the blind spot sensors 11 and 12 are arranged separately on the left back part and right back part of the automobile with one for each part. The automatic parking sensors 14, 15, 17 and 18 are arranged separately on the front left side, the front right side, the back left side and the back right side of the automobile with one for each side; the automatic parking sensors 14 and 15 also serve as auxiliary sensors of the ultrasonic blind spot monitoring system, and some automatic parking systems only have the two automatic parking sensors 14 and 15, eliminating the automatic parking sensors 17 and 18.
The sensors applied to automobiles at present, e.g., the parking sensors 16 and 13, the blind spot sensors 11 and 12 and the automatic parking sensors 14, 15, 17 and 18, are all traditional ultrasonic sensors. As the functions of the sensors vary, the detection properties required by various sensors are also different. On the requirement for the detection response speed, the reversing radar sensors (parking sensors 16 and 13) are used for the starting and parking of the automobile, so the requirement for the response speed of the sensors is relatively low. The blind spot sensors 11 and 12 are required of a relatively high response speed, because they are applied in the driving process of the automobile (including at high speeds). For the automatic parking sensors 14, 15, 17 and 18, the sensors 14 and 15, which also serve as auxiliary sensors of the blind spot monitoring system, they are required of a relatively high response speed due to their use at low, medium and high speeds.
The detection capability of a sensor is usually based on the detection of the sensor on a PVC water pipe with a diameter of 75 MM (hereinafter, the PVC water pipe with the diameter of 75 MM is referred as a standard bar) (ISO standard). The longest detection distance determines the maximum detection capability of the sensor. The stronger the detection capability of the sensor is, the longer the longest detection distance on the standard bar is, and The weaker the detection capability of the sensor is, the shorter the longest detection distance on the standard bar is.
As regards to the detection capability of the sensors, as the parking sensors 16 and 13 are used for short-distance detection,—the requirement for the detection capability of the sensors is relatively low. Generally, the ranges of the sensors are set to be about 2.5M, which is capable enough to meet the requirement of the system to detect the standard bars within about 2M.
The blind spot sensors 11 and 12 are required for detecting vehicles on the left and right lane blind areas of the exterior mirrors of the automobile, so the requirement for the long-distance detection capability of the sensors is relatively high. Generally, the ranges of the sensors are set to be 4-6 meters, and the sensors are required to detect the standard bars within 4-5M.
The automatic parking sensors 14, 15, 17 and 18 are used for detecting and recognizing the environmental state of a parking plot, so the requirement for the long-distance detection capability of the sensors is relatively high. Generally, the ranges of the sensors are set to be 4-6 meters, and the sensors are required to detect the standard bars within 4-5M.
The long-distance detection capability and the detection response speed are two most important performance indexes of an ultrasonic sensor.
When the traditional ultrasonic sensor detects an object, the range of the sensor is set as L, the ultrasonic transmission speed is set as V0 (usually 340 M/S), and the detection time for the sensor to complete a single detection is set as t. These parameters satisfy the condition: t=2*L/V0 (the ultrasonic propagation route is a round trip).
Herein, we suppose: the ranges of the parking sensors 16 and 13 are L1, wherein L1=2.5M, the time required for single detection of the traditional sensors is set as T25, i.e., the detection cycle is T25, and T25=2*L1/V0=2*2.5M/(340M/S)=0.015S, or rather 0.015 seconds; and when the sensors detect the standard bar at the distance of LG1, the schematic detection diagram is shown in FIG. 2. We suppose: the ranges of the blind spot sensors 11 and 12 and the automatic parking sensors 14, 15, 17 and 18 are L2, wherein L2=5M, the time required for single detection of the traditional sensors is set as T50, i.e., the detection cycle is T50, and T50=2*L2/V0=2*5.0M/(340M/S)=0.03S, or rather 0.03 seconds; and when the sensors detect the standard bar at the distance of LG2, the schematic detection diagram is shown in FIG. 3.
With the above assumptions, when the range is increased by one fold, the single detection time of the traditional sensors doubles, i.e., the detection cycle of the sensors doubles (T50=2*T25), but the detection response speeds of the blind spot sensors and the automatic parking sensors having high response speed requirement are lowered, thus causing serious adverse effects on the functions of the blind spot monitoring system and the automatic parking system.
In addition to the slowing down of the detection response speeds of the traditional sensors—due to the increase in the ranges, the long-distance detection capability of the blind spot sensors 11 and 12 and the automatic parking sensors 14, 15, 17 and 18 themselves is limited. This means even with the range of 5 meters, the sensors can hardly detect the standard bar at the distance of 4-5M because generally, they detect the standard bar at the distance of about 3M, and it becomes difficult for them to do so when the distance exceeds 3.5M. Therefore, the long-distance detection capability of the traditional sensors is not strong enough. The insufficiency in detection capability makes it difficult to complete and realize the blind spot monitoring function and the automatic parking function of the automobile, or even if the functions are realized, the performances of the blind spot monitoring system and the automatic parking system are compromised.
As the range increases, the single detection time of the ultrasonic sensor is also lengthened, while the detection response speed of the ultrasonic sensor slows. In order to solve this contradiction, the current solution features the conversion of the detection method of the ultrasonic sensor into the detection method of a microwave or millimeter wave sensor (probe) to improve the response speed. At present, no mature application example is available to solve this problem by improving the ultrasonic sensor itself. The microwave or millimeter wave sensor is limited in use, one main reason being that it costs much more than the ultrasonic sensor.